This invention relates to an improved composition and process for coating metal surfaces and more particularly relates to an improved composition and process for applying a protective base coating to metallic surfaces for subsequent painting. The composition and process of this invention is especially useful for base coating cold rolled steel metal surfaces.
The need for applying base coatings to metal surfaces has long been recognized in the art. One of the most important uses of base coatings is as a base for subsequent painting. Under these circumstances, the user will look to the adhesion of the paint to the metallic surface, as well as the resistance of the painted surface to humidity, salt-spray and similar tests in order to determine the corrosion quality of the painted article. Where forming is to be employed subsequent to painting, the user will also be concerned with the formability of the metal and the corrosion resistance of the metal after the metal has been formed.
In the past, difficulties have often been encountered in developing a composition and method for treating metal surfaces which produces an end product which, when painted, exhibits satisfactory formability adhesion and corrosion characteristics. High coating weights were required for corrosion protection while low coating weights were required for formability. Generally speaking, conventional compositions and methods for treating metal surfaces have involved multi-stage chemical treatments of the metal with water rinsing after each treatment. However, multiple-stage treating involves additional personnel, inter-stage contamination problems, extended line length, and problems with regard to disposal of rinse water.
The present invention provides a single-application, no rinse, composition and method for the treatment of bare metal surfaces for the purposes of forming a corrosion-resistant base coating thereon. The base coating of the present invention provides satisfactory corrosion protection at a low coating weight while still providing satisfactory formability. The improved coating may be provided on various metal surfaces, but is especially useful on cold rolled steel. The coating imparts to the metal a high degree of corrosion resistance and paint applied thereto is satisfactorily adherent. The process of the present invention minimizes inter-stage contamination problems, line length and problems associated with disposal of process chemicals.
Further understanding of the present invention will be had from the following description and claims. All parts and percentages herein are by weight unless otherwise indicated.